This invention is related to metallic seats for gate valves which are designed to operate in a significantly elevated thermal environment and to carry heated fluids. More particularly this invention is related to metal gate valve seats which are sufficiently flexible to maintain a fluid-tight seal with a gate member when the valve is influenced by a high temperature thermal service environment and/or influenced by bending forces which will deform the valve body.
By way of background, the major obstacles involved in constructing valves for operation at high temperatures are concerned with deformation of the valve body in the area of the seats which makes it difficult to achieve sealing with the gate member. When a valve is manufactured the sealing surfaces of the seats, the seat pockets, and the gate are machined to be essentially flat. However, these parts do not remain flat once the valve is in operation carrying a high temperature lading or where it is located in a relatively high temperature environment. Generally, a valve is in a high temperature environment because it is carrying a high temperature lading. For purposes of this description high temperature denotes any temperature above approximately 300.degree. F. When a valve carries a high temperature lading, a thermal gradient is established between the center portion of the valve and its exterior which is cooler. This thermal gradient causes warping or deforming of the valve body and the seats, therefore, the previously flat surfaces are no longer flat and will no longer seal as they would at room temperature. In addition to deteriorating the seal because of the non-flat surfaces, the warping also causes excessive pressure to be exerted on the gate member along its opposite sides of the transverse extremities of the seats. The result of this excessive pressure is galling of the gate in the zones which are subjected to the high pressures.
In regard to the metal valve seat art, several all metal seat constructions are known for gate valves. However, these seat constructions do not have the combination of critically important features which are present in the subject invention. An early attempt at a flexible metal face seal is shown in the patent of Wolff, U.S. Pat. No. 1,756,616 issued Apr. 29, 1930. This seat is formed integral with the valve body and includes a flexible lip, one side of which is the sealing surface that contacts the gate. Because this seat is part of the body it will not compensate for thermally induced deformations of the valve body. The patent of Stevens, U.S. Pat. No. 1,489,857 issued Apr. 8, 1924, discloses a metal seal having a rigid inner member and a flexibly supported outer seal member. In the Stevens patent the rigidly supported inner member is secured to the valve body and can be deformed with the valve body. Thus, it will be subject to the disadvantages of rigid seats discussed above. Although this seat has a flexible element, its location will let line pressure move it away from the gate once the inner member leaks. The patents of Holzer, U.S. Pat. No. 2,772,848 issued Dec. 4, 1956, and Bryant, U.S. Pat. No. 2,777,664 issued Jan. 15, 1957, also disclose metal seats. Both of these patents disclose seat constructions which have a flexible element supporting the face seal that will flex some to accommodate distortions of the valve body. In both of these seat constructions this allowance for deformation would only be possible in slab gate valves and would not function in valves where the gate expands laterally for sealing because such lateral expansion with these seat constructions would urge the seats into essentially rigid contact with the valve body, thus obviating the effectiveness of the flexible element.